1. Field of the Invention
The invention relates to a method and apparatus for inserting appropriate dialling intervals between digits of dialling sequences stored in an abbreviated dialling or redial store in a telephone set.
2. Description of the Related Art
If telephone subscriber stations are connected to a private branch exchange, after connection to the PBX line has been established an interruption of the continued dialling is often required until dialtone is received for access to the public exchange line. This dialling interval must also be provided when the dialed number is stored in a register and is to be read again upon dialling by means of such register. Modern telephone apparatus often comprises key dialling devices, by means of which long subscriber numbers are stored in a register and can be requested by depression of a particular key. Such register dialling also provides performance features such as dialling repetition or redial, abbreviated dialling, target dialling, direct dialling or name dialling.
Published West German patent application No. DE-OS 2940490 discloses an automatic interval generator for dialling devices, in which the dialling information supplied by a keyboard is stored in a store. That information includes the subscriber number and direct exchange identification digits. By means of a comparison device, when dialling information is supplied a check is made whether the digit supplied is identical to a stored direct exchange identification digit. If there is such an agreement between a supplied digit and a direct exchange identification digit, after such digit is dialled an interval criterion is supplied by the store to the digit interval generator. As a result, such an interval is inserted prior to the succeeding digits of the sequence of dialling digits. The dialling interval can be a fixed interval or can be shortened by means of an additional dialtone detection circuit upon the arrival of dialling tone.
Published West German patent application No. DE-OS 2426690 discloses an automatic subscriber dialling device, in which, when dialling information is entered, an interval for identification of dialling tone is set so that an additional coded signal can be supplied between two digits of the subscriber number. By means of the additional code signal, upon the occurrence of the latter the transmission of the stored subscriber number is stopped. The command to continue transmission of the stored subscriber number can be given by the subscriber by hand or by a dialling tone identification device connected to the subscriber line.
In the aforementioned method, dialling intervals having a define maximum length are supplied or else a dialling tone detection circuit determines the instant for continued dialling. In the case of an erroneous operation by the user or replacement of an extension station, it cannot always be avoided that erroneous dialling will occur. Furthermore, since not every user is capable of carrying out a reprogramming of the dialling interval, this may involve high cost.
Published West German patent application No. DE-PS 2401276 further discloses a circuit arrangement for storing subscriber numbers that can repeatedly be requested. In such circuit arrangement time-dependent switching means are provided which respond to entry of successive digits at an interval exceeding a given minimum interval therebetween. Such time-dependent switching means may be repeatedly triggerable monostable trigger stages or counters, whose output signals are supplied to an interval coding device. The interval coding device delivers a particular signal--that cannot be interpreted as dialling information--for lengthening the dialling intervals, which is stored in the intermediate store for subscriber numbers. By means of such a circuit arrangement, the interval length can be measured and also be varied in a simple manner, but there is additional cost for the time-dependent switching means and the high storage capacity of the intermediate store for dialling digits, in which each subscriber number is stored having digits between which there is an interval exceeding the given minimum interval.
As used herein, the term "interval" signifies a dialling interval of a length exceeding the normal interval between dialling digits and which is included in a dialling sequence following a digit therein which identifies the required line connection.